Is creating ViewModels in Web API a bad practice?

by SamuraiJack   Last Updated October 09, 2019 18:05 PM

So, somebody at work who is twice as experienced than I am, told us that we must not create ViewModel classes within Web API. (We are using Angular for UI)

In his opinion ViewModel is ASP.NET MVC approach. And we must come out of it when using Web API.

Here is my argument for using ViewModel in WebAPIs:

Database Tables


name | phone | categoryId |...Col15


categoryId | Description

C# Class

Class Employee
 public string name {get;set;}
 public phone {get;set;}
 public categoryId {get;set;}
 //...till col15

If your UI page shows only :

 name | phone | categoryId | CategoryDescription

Wouldn't it make sense to create a ViewModel class in API that has only these 4 properties as opposed to all 15 properties? The JSON that will be returned by this class will only have 4 properties instead of 15 properties where 11 of them contain null value.

If there is a list of say 100 Employees it would mean 1100 empty json properties that will be sent to the UI if we use original Employee class instead of a ViewModel class.

Also, if we stick to our original Employee class we might have to do one of the following:

  1. CategoryDescription must be added to original Employee class
  2. Make a second API call from UI to get the description.

Answers 1

In principle, frontend frameworks such as Angular are best used against a REST API, which implies that you don't have viewmodels and simply expose your resources as they are.

However, from the sound of it, you're not using a REST API but rather an API tailored to the needs of the frontend application. I say this because you mention that the API specifically omits 11 out of 15 properties because it knows that the frontend won't need them for this particular case.

If that is the case, then your API is inherently aware of your frontend application views, and you are effectively working with viewmodels. It seems like your colleague is simply suggesting to not make an explicit viewmodel and instead is trying to reuse existing DTOs but with properties that are intentionally kept empty, which is not good practice.

So, to summarize, the "no viewmodels" stance works if you have a REST API. If you have an API which handles custom requests and automatically redacts data because it knows what the frontend will/won't display, then the "no viewmodels" stance is contradictory to how the API is being developed.


In his opinion ViewModel is ASP.NET MVC approach.

MVC stands for Model-View-Controller. MVC has no viewmodels. MVVM (Model-View-ViewModel) however does have viewmodels.

I'm not sure whether this conflation is on your side or on your colleague's side, but it's nigh impossible to productively discuss the use of viewmodels (or lack thereof) if either party can't distinguish MVC and MVVM.
At the very least, you'd be using the wrong name (viewmodel vs model), which makes it really hard for other people to provide accurate feedback based on your explanation.

October 09, 2019 17:23 PM

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